[21.09] Doppler Tomography of Accretion Regions in Algol Binaries

The technique of Doppler Tomography has been used to reconstruct images of
the accretion regions in the short-period Algol-type binaries RS Vul, U Sge, U CrB, $\beta$ Per, S Equ, TX UMa and SW Cyg. H$\alpha$ difference profiles of these systems show single and/or double-peaked
emission features at most phases outside of primary eclipse, and absorption features throughout primary eclipse, except at mid-eclipse. A Back Projection Tomography code was used to generate the sources of H$\alpha$ emission in the orbital plane of the binary. The tomograms show clear evidence of a gas flow along the predicted free-fall path of the gas stream as well as asymmetric disk-like structures both on and around the mass gainer. Another source of H$\alpha$ emission is associated with the cool magnetically active secondary. The gas stream source was strongest in U CrB while the disk emission was strongest in SW Cyg. Observations of U Sge in June 1993 show evidence of a strong almost Keplerian accretion disk, but in June 1994 the emission from this binary was predominantly from the gas stream. The disk emission seen in the Algols is reminiscent of that seen in the cataclysmic variables (e.g., U Gem).